The present invention relates to electrical rotating machine systems or wind turbine systems.
In recent years, power generation systems that use natural energies such as wind power have been getting a lot of attention for the sake of the prevention of global warming. There are many examples that a rotor excitation type electrical rotating machine is used for wind power.
In the case where an exciter electrical rotating machine is used, it is necessary to supply excitation power to rotor windings in a rotor that is rotating while the exciter electrical rotating machine is running. An ordinary exciter electrical rotating machine is equipped with slip rings and brushes used for supplying electric power to the rotor windings, and therefore the brushes are set up to establish contact with the slip rings to pass electric currents. However, because a power generating operation deals with a great deal of energy, if slip rings and brushes are installed to supply excitation power for the power generating operation, the brushes are rapidly worn away, therefore it is necessary to periodically maintain the brushes. However, in a wind turbine system, because it is necessary to maintain an exciter electrical rotating machine that is housed in a small space, that is, in a nacelle installed on the top of a windmill tower, a method for maintaining the exciter electrical rotating machine more easily has been required.
An example of a brushless doubly-fed electrical rotating machine is disclosed in Japanese Unexamined Patent Application Publication No. 2002-95288. This patent application publication describes the brushless doubly-fed electrical rotating machine in which a wound rotor type induction machine is connected to a fly wheel that stores electric power in the form of rotational energy; the rotor winding of the wound rotor type induction machine is directly and electrically connected to the rotor winding of an exciting wound rotor type induction machine; the rotors of both wound rotor type induction machines are mechanically connected to each other; and the stator winding of the exciting wound rotor type induction machine is connected to a power converter that is disposed outside both induction machines.
The number of poles of the wound rotor type induction machine and that of the exciting wound rotor type induction machine are different from each other, and both wound rotor type induction machines are configured in such a way that the synchronous speed of the exciting wound rotor type induction machine is higher than that of the wound rotor type induction machine.